1. Field of the Invention:
The invention relates to a first-wall component of a fusion reactor. The first-wall component contains at least one heat shield with a closed or open lead-through formed of a graphitic material and a cooling tube through which a coolant flows and which is at least partially material-bonded to the heat shield and is formed of a material having a thermal conductivity>200 W/m·K.
A typical example of the use of first-wall components of this type is diverters and limiters that are exposed to the high thermal loads of more than 10 mW/m2. First-wall components normally contain a heat shield and a heat-dissipating region. The material of the heat shield must be compatible with plasma, have high resistance with respect to physical and chemical sputtering, possess a high melting point/sublimation point and be as resistant as possible to thermal shock. In addition, they must also have high thermal conductivity, low neutron activatability and sufficient strength/fracture toughness, along with good availability and acceptable costs. In addition to refractory metals, such as, for example, tungsten, and graphitic materials (for example, fiber-reinforced graphite) best fulfill this diverse and sometimes contradictory requirement profile. Since the energy flows from the plasma act on these components over a lengthy period of time, first-wall components of this type are typically cooled actively. The heat discharge is assisted by heat sinks that contain, for example, copper or copper alloys and which are usually mechanically connected with the heat shield.
First-wall components may be implemented in a varying configuration. A customary design is in this context is what is known as a monobloc design. In the monobloc design, the first-wall component contains a heat shield with a concentric bore. The heat shield is connected to the cooling tube via this concentric bore.
First-wall components have to tolerate not only thermally induced, but also additionally occurring mechanical stresses. Such additional mechanical loads may be generated via electromagnetically induced currents that flow in the components and interact with the magnetic field of the surroundings. In this case, high-frequency acceleration forces may arise, which have to be transmitted by the heat shield, that is to say, for example, by the graphitic material. However, graphitic materials have low mechanical strength and fracture toughness. In addition, during use, neutron embrittlement occurs, thus resulting in a further increase in the sensitivity of these materials with respect to crack introduction. Fiber-reinforced graphite (CFC) is usually employed as the graphitic material. The fiber reinforcement is in this case disposed three-dimensionally and linearly. The architecture of the fibers gives the material different properties, depending on the orientation. CFC is usually reinforced in one orientation by Ex-pitch fibers that have both the highest strength and also thermal conductivity. The other two orientations are reinforced by Ex-PAN fibers, one direction typically only being needled.
Thus, whereas CFC has a linear material architecture, the heat shield/cooling tube connection geometry is circular. On account of the different coefficients of thermal expansion of the materials used, during the production process a stress build-up occurs which may lead to cracks in the CFC. These cracks can be detected, if at all, only by highly complicated methods because of the geometric conditions and the material combination used. This presents corresponding problems against the background of a nuclear environment for such components, above all also because cracks/peelings are seen as a possible trigger for a major incident. Despite complicated year-long development activity in the field of first-wall components, the components available hitherto do not optimally fulfill the requirement profile.